Q. A beaker full of hot water is kept in a room. If it cools from 80$^{\circ}$C to 75$^{\circ}$C in $ t_1 $, minutes, from 75$^{\circ}$C to 70$^{\circ}$C in $t_ 2$ minutes and from 70$^{\circ}$C to 65$^{\circ}$C in $ t_3 $ minutes, then
AIPMTAIPMT 1995
Solution: